1. Field of the Invention
The present invention relates to a mounting structure produced by flip-chip mounting a semiconductor device such as an integrated circuit chip onto a substrate, and a method for producing the same.
2. Description of the Related Art
Heretofore, in mounting a semiconductor device onto input/output terminal electrodes of a circuit board, one often utilizes the wire bonding method by soldering. In recent years, however, owing to scale reduction of a package of the semiconductor device and increased number of connection terminals, an interval between the connection terminals is becoming narrower, making it more and more difficult to perform wire bonding by soldering.
Therefore, in recent years, a structure is proposed in which the semiconductor device such as an integrated circuit board chip is directly mounted on the input/output terminal electrodes of the circuit board for scale reduction and effective utilization of a mounting area.
Above all, a structure in which a semiconductor substrate is flip-chip mounted facedown on a circuit board is regarded as being a useful structure because a collective electrical connection can be established between the semiconductor device and the circuit board in addition to large mechanical strength after establishing connection.
Next, an example of the flip-chip mounting method will be described with reference to FIG. 5. First, bump electrodes 3 are formed on pad electrodes 2 of an IC board 1 constituting a semiconductor device 4 by a known method. Then, an electrically conductive adhesive 7 is supplied to input/output terminal electrodes 6 of a circuit board 5 to which the semiconductor device 4 is to be mounted or to the bump electrodes 3. Further, an adhesive 8 is applied to either one of the semiconductor device 4 and the circuit board 5. The adhesive 8 is disposed in a region which is located on a surface facing to the other (i.e. the rear surface of the semiconductor device 4 or the mounting surface of the circuit board 5) and which is not involved in electrical connection between the two.
After making the above-mentioned preparations, the semiconductor device 4 is disposed on the circuit board 5. At this time, the semiconductor device 4 is positioned so that the bump electrodes 3 face to the input/output terminal electrodes 6. Thereafter, the adhesive 7 and the electrically conductive adhesive 8 are cured. In this state, a test of electrical properties is performed on the semiconductor device 4 and the circuit board 5. If the test results are good, a sealing resin 10 is supplied to a connecting place or a gap between the semiconductor device 4 and the circuit board 5 for curing, thus completing a mounting structure 9.
In recent years, in the field of mounting, in accordance with scale reduction and weight reduction of electronic equipments, a multi-chip module (hereafter referred to as MCM) is proposed in which a plurality of semiconductor devices are flip-chip mounted onto a circuit board to form a module. In such an MCM, all of the plurality of semiconductor devices operate to function as one module. For this reason, in the mounting structure 9 constituting the MCM, the following point is of importance in terms of the costs and the good-product ratio of the mounting structure and the yield in the mounting process.
Whether the semiconductor device 4, whose electrical properties are found to be poor in an electrical property test conducted before sealing with a sealing resin 10, can be replaced easily or not, i.e. the repairability of the semiconductor device 4, is important.
However, according to the conventional method, the electrical property test is conducted on the semiconductor device 4 and the circuit board 5 after the adhesive 7 is cured. Therefore, if the test results are found to be poor, the poor one is peeled off from the other one against a bonding force of the adhesive 7. For this reason, fragments of the poor one often adhere to the other reutilizable one, making it substantially impossible to reutilize the other one.
Accordingly, a major object of the present invention is to reduce the costs and to increase the good-product ratio and the yield by improving the repairability of the mounting structure.
In order to achieve the aforementioned object of the present invention, the first one of the present invention is directed to a method of producing a mounting structure comprising: a connecting step of flip-chip mounting a semiconductor device onto a substrate; a bonding step of bonding a region of said semiconductor device to a region of said substrate by means of an adhesive, each of said regions not being involved in electrical connection; a testing step of performing a test of electrical properties on said semiconductor device and said substrate that are connected to each other; and a separating/sealing step of separating said semiconductor device from said substrate after heating a bonding place of said adhesive up to a temperature higher than a glass transition point or a melting point of said adhesive if it is determined that said electrical properties are poor in said testing step, and sealing said semiconductor device and said substrate by means of a sealing resin if it is determined that said electrical properties are good in said testing step.
This allows the testing step to be carried out in a state in which the semiconductor device and the substrate are firmly bonded to each other by the adhesive, so that the electrical properties of the semiconductor device and the substrate can be tested with high precision. Furthermore, the adhesive can be brought into a softened state if a heating process performed in the case where the electrical properties are found to be poor, i.e. a process of heating a bonding place of the adhesive up to a temperature above the glass transition point or the melting point of the adhesive, is carried out. If the semiconductor device is separated from the substrate in this state, separation of the semiconductor device from the substrate can be carried out easily without causing damages to the semiconductor substrate or the substrate.
In the present invention, an electrically conductive adhesive used in said connecting step preferably comprises a thermoplastic resin. This reduces the possibility of damaging an electrical connecting portion of the semiconductor device and an electrical connecting portion of the substrate in separating the semiconductor device from the substrate because the electrically conductive adhesive comprising the thermoplastic resin has a comparatively low bonding strength. Here, by using an electrically conductive adhesive comprising a thermoplastic resin, it is feared that the electrical property test of the semiconductor and the substrate will be unreliable in the testing step. However, in the present invention, since the testing step is carried out after allowing the semiconductor device and the substrate to be bonded to each other comparatively firmly by the adhesive in the bonding step, there is no fear that the electrical property test of the semiconductor and the substrate will be unreliable in the testing step.
In the present invention, the adhesive used in the bonding step preferably comprises a thermosetting resin. This allows the testing step to be carried out after more firmly bonding the semiconductor device and the substrate to each other by the adhesive in the bonding step, because the thermosetting resin is an adhesive having a comparatively high bonding strength. Therefore, reliability of the electrical property test in the testing step is further improved.
In the present invention, the adhesive is preferably cured at a temperature lower than the glass transition point of the adhesive in the bonding step. This allows the adhesive to be softened at a temperature lower than the inherent glass transition point of the adhesive, thereby lowering the temperature for a heating process carried out in the separating/sealing step (the temperature at which the adhesive is brought into a state similar to the state of glass transition) to facilitate the process.
In the present invention, the adhesive used in the bonding step preferably comprises a low melting point metal. This allows the testing step to be carried out after more firmly bonding the semiconductor device and the substrate to each other by the adhesive in the bonding step, whereby the reliability of the electrical property test in the testing step is further improved.
In the present invention, if it is determined that the electrical properties are poor in the testing step, the semiconductor device is separated from the substrate preferably by applying a torsional force to the adhesive in the separating/sealing step. This allows the step of separating the semiconductor device from the substrate, which step is performed as a next step after the electrical properties are found to be poor, to be carried out reliably and with a comparatively small force.
The second one of the present invention is directed to a method of producing a mounting structure comprising: a connecting step of flip-chip mounting a semiconductor device onto a substrate; a bonding step of bonding a region of said semiconductor device to a region of said substrate by means of an adhesive, each of said regions not being involved in electrical connection; a peeling permitting layer forming step of forming a peeling permitting layer on an adhesive abutting region of said semiconductor device and/or an adhesive abutting region of said substrate, said peeling permitting layer forming step being performed before said bonding step; a testing step of performing a test of electrical properties on said semiconductor device and said substrate that are connected to each other; and a separating/sealing step of separating said semiconductor device from said substrate if it is determined that said electrical properties are poor in said testing step, and sealing a gap between said semiconductor device and said substrate by means of a sealing resin if it is determined that said electrical properties are good in said testing step.
This allows the testing step to be carried out in a state in which the semiconductor device and the substrate are firmly bonded to each other by the adhesive, so that the electrical properties of the semiconductor device and the substrate can be tested with high precision. Furthermore, if it is determined that the electrical properties are poor in the testing step, the peeling permitting layer allows the semiconductor device and the substrate to be separated from each other easily without leaving a residue to the other one of the semiconductor device and the substrate and without causing damages to each other.
The peeling permitting layer may be, for example, a fluororesin layer or a layer having a bonding force that weakens by a predetermined process. Examples of the layer having a bonding force that weakens by a predetermined process include a substance having a bonding force that weakens by swelling through reaction with a solvent, a substance having a bonding force that weakens by foaming through a heating process, and a substance having a glass transition point or a melting point lower than the adhesive.
As described above, the present invention allows a repairing work to be carried out without causing damages to the place involved in the electrical connection.
In addition, by further forming a peeling permitting layer, the repairing work can be carried out without leaving a residue of the adhesive, so that the semiconductor device and the circuit board can be reutilized without a cleaning process after the repairing work.
Furthermore, the force needed in the repairing work can be reduced to half by applying a torsional force after forming the adhesive at a single position.